1. Field of the Invention
The present invention relates to improvement of a process for producing polyolefins. More specifically, the present invention relates to a process for producing polyolefins having a high stereoregularity and/or having broad molecular weight distribution, in high yield.
2. Related Art
Heretofore, a production of polyolefins has been widely conducted by the use of a Ziegler-type catalyst. Several attempts to improve the Ziegler type catalysts have been made to obtain highly active catalysts or to obtain polyolefins having a high stereoregularity.
For example, JP Patent Appln. Laid-Open No.(hereinafter referred to as Kokai) 57-63310 and Kokai 57-63311 disclose a process for polymerizing alpha-olefin having at least three carbon atoms, utilizing a catalyst which consists of a solid catalyst component comprising a magnesium compound, a titanium compound and electron donor compound; an organoaluminum compound; and an organosilicon compound having a Si--O--C linkage to improve stereoregularity. However, these processes are not always sufficient enough to obtain polymers having a high stereoregularity in high yield. Further improvement has been desired.
Kokai 54-94590 discloses, as a method of producing polymers with a high stereoregularity in high yield, a process for producing polyolefins, utilizing a solid catalyst component comprising a magnesium compound, a titanium compound and an electron donor compound; an organoaluminum compound; and an organosilicon compound having a Si--O--C-- linkage. Kokai 62-11706 teaches a polymerization process using, as the organosilicon compound, a compound having a branched hydrocarbon residue. These processes can produce polymers with a high stereoregularity in high yield; however, the obtained polymers have narrow molecular weight distribution resulting in poor moldability. In the case of making large molded articles, it is difficult to obtain desired strength.